The present invention pertains generally to the field of apparatus for the removal of flash from molded parts. In particular, the present invention pertains to the removal of flash from miniature molded parts, which heretofore have not been satisfactorily economically deflashed.
The removal of flash, which is the unwanted, generally thin flange of molded material adherring to a molded part, resulting from the seeping of molten material between the faces of the mold during the molding process, has generally been performed in the prior art by an abrasive process. The parts are first cooled to the embrittlement temperature of the material from which the parts are made, and are then rotated in a tumbling machine, or shaken in a shaking machine together with the abrasive media. The flash, being of substantially less thickness than the rest of the part, is broken off by the impingement by the media particles, due to its embritted state. A wide range of media have been used in the prior art, including metal shot, sand and nails. While this prior art method has been successful with larger parts such as rubber hose fittings, it has not been successful in deflashing smaller rubber parts having dimensions of fractions of inches.
The deflashing problem has been complicated by the use of very hard and durable materials such as Delrin and glass filled nylon in molding small parts. Frequently, the molded parts are intended for use in close tolerance applications in which a very small amount of flash would render the parts unusable. In the computer industry, for example, small molded parts for use in computer assemblies may require that the flash be less than 0.0005 inches. In such cases, the prior art deflashing apparatus has been entirely unsuccessful, and it has been necessary for workers to deflash each individual part by hand with a razor blade, frequently with the aid of a microscope. Individual handling of many thousands of small parts obviously leads to a very significant labor cost, often many times the original cost of the part.
In the deflashing of relatively small parts, of any material, the prior art tumbling machines have not been very effective. Limited success has been achieved in the prior art through the use of a paint shaker type of machine. The product and media, which may be nails, walnut shells, metal shot, or the like, are placed inside a paint can or bucket which has been clamped into the shaker machine. While this prior art method has met with some limited success, it suffers from the disadvantages of requiring a relatively long shaking time, high breakage and damage rates to the product, and inability to produce uniformly close tolerances.
The present invention provides apparatus which uses a similar shaking motion, but with a specially configured shaking container so as to provide a special tossing and intermixing action of the product and media, resulting in operation and efficiency which is vastly improved over the prior art. The present invention also provides a specially configured cryogenic vessel for use with the deflashing apparatus, which greatly improves efficiency when liquified gases are used to cool the product.
Another problem existing in the prior art is the rapid formation of rust on steel media in cryogenic deflashing processes. At the end of the process, moisture from the air condenses on the cold media particles, causing them to rust. This rusting can lead to discoloration of subsequently deflashed products, particularly in the case of white nylon parts, in which case it may be impossible or impractical to wash the discoloration off the product. This problem in the prior art has lead to the discarding of steel media for cryogenic deflashing after one use, and the attendant increased costs. According to another feature of the present invention, this rust problem is overcome, without foregoing one of the main advantages of steel or iron media, which is the capability of using magnetic separation of the media from the product. According to this aspect of the invention, chrome plated tacks are provided for deflashing the product. The chrome plated tacks are not subject to a rust problem, they retain their ability to be magnetically separated, and they have sufficient hardness to maintain a sharp point for deflashing the harder low embrittlement temperature products, and maintain their sharp point through many deflashing cycles.